Impact of packaging film colour on phytosterol photooxidation in safflower seed oil

This study investigated the protective effects of five colored PET films against phytosterol (PS) oxidation in vegetable oil. The transparent film demonstrated the lowest inhibition rates for the formation of phytosterol oxidation products (POPs) among the five coloured films, which inhibited PS oxidation solely by reducing light intensity. In contrast, the blue film exhibited superior light barrier characteristics, effectively blocking wavelengths corresponding to ultraviolet light and chlorophyll excitation bands. This dual mechanism significantly reduced both auto-oxidation and type II photooxidation pathways of PS. Consequently, the blue film increased inhibition rates for POPs (7α-OH-PS, 7β-OH-PS, 5α,6α-epoxy-PS, 7-keto-PS, 6β-OH-PS, and 5β,6β-epoxy-PS) from 22.12 %, 13.66 %, 15.08 %, 12.16 %, 12.93 %, and 10.70 % to 76.60 %, 75.29 %, 79.40 %, 75.41 %, 77.56 %, and 75.33 %, respectively. Mechanistic analysis revealed that the blue film's enhanced protection for PS oxidation originated from its inhibition of C7 pathway-mediated POP generation. While red, yellow, and green films operated through similar protective mechanisms, their efficacy varied significantly. The overall protective performance was ranked as follows: red ≈ blue > yellow > green > transparent. These findings provide critical insights for developing optimized packaging solutions to inhibit PS oxidation in lipid-containing food products.